The present invention relates to implantable medical leads generally and more particularly to multi-conductor implantable leads employing coiled conductors that extend to a distal portion of the lead.
In the context of implantable pacing and cardioversion leaves, it is desirable that the lead be provided with a tensile member that extends along the entire length of the lead. Such a tensile member is desirable in that it prevents disassembly of the lead in response to traction forces applied to the proximal end of the lead, in conjunction with removal of the lead after implant. One approach to providing such a longitudinal reinforcement is set forth in U.S. Pat. No. 5,231,996 issued to Bardy et al, which suggests adding a nonconductive tensile reinforcing member from the connector assembly at the proximal end of the lead to an electrode located at the distal end of the lead. An alternative approach to providing a tensile member extending the length of the lead is set forth in U.S. patent application Ser. No. 08/938,269 by Bischoff et al., filed on Sep. 27, 1997, which discloses a structure in which the tip and ring electrode are mounted to a rigid plastic head and the conductor extending from the proximal end of the lead to the ring electrode is mechanically interconnected with the rigid plastic head. The disadvantage with the approach set forth in the Bardy et al patent is that it requires an additional tensile member extending the entire length of the lead, which in turn generally increases in the required diameter of the lead body over the majority of its length. Although the approach set forth in the above-cited Bischoff et al. application avoids the problem of an increased lead diameter, it requires a rigid member interconnecting the ring electrode and the tip electrode in order to provide tensile reinforcement all the way to the distal electrode. In the context of tined leads or other leads in which a coiled conductor is used to connect to the tip electrode and in which the portion of the lead body intermediate the tip electrode and electrodes located proximal thereto is typically fabricated out of a flexible elastomer, the approach of the Bischoff et al. application is not readily applicable.